Book	FZJ-2021-04324

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Surface Acoustic Waves in Strain-EngineeredThin (K,Na)NbO3 Films: From Basic Research to Application in Molecular Sensing

Liang, S. (Corresponding author)FZJ*

2021
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich
ISBN: 978-3-95806-571-0

Please use a persistent id in citations: http://hdl.handle.net/2128/29598  urn:nbn:de:0001-2022011221

Abstract: In this work we demonstrate that in thin film systems, the energy of surface acoustic waves(SAW) is more concentrated on the surface compared to bulk system, which makes this systemextremely sensitive to any perturbation on the surface. On this basis we developed a thin filmSAW system with extremely high sensitivity to any mass loading. Due to its outstandingpiezoelectric properties, KxNa1-xNbO3 (KNN) was chosen as a candidate for the thin filmsystem. Using epitaxial strain the piezoelectric properties were tailored in order to improvethe SAW signal and sensitivity. Finally, a thin (~ 30 nm) film KNN based SAW sensor wasdeveloped which allows to detect monolayer deposition of organic molecules.For the deposition of epitaxial KNN films, two methods—metal organic chemical vapordeposition (MOCVD) and pulsed laser deposition (PLD)—were used. A series of scandates,DyScO3 (DSO), TbScO3 (TSO), GdScO3 (GSO), and SmScO3 (SSO), were chosen as substrates withdifferent lattice mismatch with respect to the KNN films and therefore different levels ofcompressive strain. According to X-ray analysis (reciprocal space mapping (RSM)), theMOCVD-prepared KNN samples show perfect epitaxial growth, whereas the PLD-preparedsamples are epitaxy but show an onset of plastic relaxation. The MOCVD samples exhibit atypical conventional ferroelectric behavior with hardly any frequency dispersion of theferroelectric phase transition. In contrast, the PLD samples show textbook-like relaxorbehavior with a frequency dispersive ferroelectric phase transition. It seems that the higherparticle energy of PLD leads to microscopic composition inhomogeneities which results in theformation of polar nanoregions (PNR).Due to the compressive strain, the phase transition temperatures of MOCVD and PLD samplesare shifted from TC ≈ 693 K for unstrained KNN to lower temperatures. A “square model” isfirst applied to analyze the strain dependence of the phase transition temperature. The phasetransition temperatures of MOCVD samples show a perfect linear dependence on compressivestrain, whereas the PLD samples show no clear dependence. In order to improve the model, a“normal lattice model” (NLM) is proposed which is based on the Poisson effect. In the newmodel, the strain of the film is represented by the vertical lattice parameter of the KNN film.The phase transition temperatures of both MOCVD and PLD samples show a perfect linearitywith slightly different slopes as function of vertical lattice parameter. This supports the use ofthe new model for the description of the strain dependence of the phase transitiontemperature.

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Contributing Institute(s):

1. Bioelektronik (IBI-3)

Research Program(s):

1. 5241 - Molecular Information Processing in Cellular Systems (POF4-524) (POF4-524)

Appears in the scientific report 2021

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